Overvoltage protection device

ABSTRACT

An overvoltage protection device capable of protecting a power supply line and including in parallel a break-over diode, a controlled switch, and a circuit for controlling the switch.

BACKGROUND

Technical Field

The present disclosure relates to an overvoltage protection device, andmore specifically to an overvoltage protection device capable ofprotecting a power supply line.

Description of the Related Art

An overvoltage protection device is a component or circuit which turnson when the voltage thereacross exceeds a given threshold, calledbreakdown voltage, and generally designated as V_(BR).

A first type of protection component is of avalanche diode type, with acurrent-vs.-voltage characteristic illustrated in FIG. 1. When thevoltage across this component exceeds breakdown voltage V_(BR), thecomponent turns on. Ideally, the voltage across the component remainsequal to V_(BR) while the current increases. Indeed, as shown in FIG. 1,the characteristic is not vertical and the voltage across the componentexceeds value V_(BR) while the overvoltage is absorbed, that is, acurrent I of strong value crosses the component.

A disadvantage of this type of component is that during the overvoltageabsorption phase, the voltage across the component remains greater thanor equal to breakdown voltage V_(BR), that is, during this phase, thecomponent has to absorb a power greater than V_(BR)×I. This results inhaving to form a component having sufficiently large size to be able toabsorb this power without being destroyed. Currently, for voltagesV_(BR) greater than 100 volts, for example, on the order of 300 volts,this results in component sizes greater than several cm², for example,on the order of 10 cm². Such components are however made in the form ofa stack of diode chips, for example, a stack of fourteen elementarycomponents each having a surface area of 8.6×8.6 mm² to reach a 430-Vbreakdown voltage. Such components are thus expensive and bulky.

A second type of protection component is of break-over type, of Shockleydiode type, or of gateless thyristor type. The current-vs.-voltagecharacteristic of a break-over component is illustrated in FIG. 2. Whenthe voltage across the component exceeds breakdown voltage V_(BR), thisvoltage rapidly drops and then follows a substantially verticalcharacteristic I.

An advantage of this second type of component is that the powerdissipated by the overvoltage in the component is low as compared withthe power dissipated in a device of avalanche diode type, given that thevoltage across the component is very low during the overintensity flow.A disadvantage of this second type of component is that, as long asthere is a voltage across the component, said component remains on, theprotection component only turning back off if the voltage thereacross issuch that the current in this component becomes smaller than a holdcurrent I_(h). For a protection component having its breakdown voltageV_(BR) approximately ranging from 50 to 1,000 volts, this hold currentcurrently has a value approximately ranging from 100 mA to 1 A accordingto the breakdown voltage of the component.

Accordingly, break-over type protection components are reserved forcircuits where these components are intended to protect a line having anoperating voltage crossing zero values—this being in particular true fora data transmission line.

As illustrated in FIG. 3, if a line L1 forming a power supply lineconnected to the output of a power supply device such as a solar powerplant 10, for example connected to an inverter 12, is desired to beprotected, a break-over protection component can normally not be usedsince, after the occurrence of an overvoltage, for example correspondingto a lightning surge on line L1, the voltage on line L1 remains positiveand the protection component remains conductive.

As illustrated in FIG. 4A, after application of the overvoltage, voltageV_(DC) at the output of power supply source 10 is short-circuited and ashort-circuit current I_(sc) flows therein. The source sees across itsterminals internal resistance Ri and on-state resistance R_(D) of theprotection diode. A voltage V_(D)=V_(DC)(R_(D)/(Ri+R_(D))) then existsacross the protection diode.

FIG. 4B shows a portion of the characteristic curve of the diodecorresponding to this specific case. In most practical configurations,potential V_(D) corresponding to short-circuit current I_(SC) is muchgreater than voltage V_(h) corresponding to hold current I_(h) of thebreak-over component. As an example, for a 150-mA hold current I_(h),voltage V_(h) may be on the order of 2 V. It is thus a priori notpossible to use a break-over component to protect a D.C. power supplyline. Protection devices of avalanche diode type, which have significantsurface areas and thus a high cost, thus are used.

It is here desired to overcome this disadvantage.

BRIEF SUMMARY

Thus, an embodiment provides an overvoltage protection device capable ofprotecting a power supply line comprising in parallel a break-overdiode, a controlled switch, and a circuit for controlling the switch.

According to an embodiment, the break-over diode is in series with anavalanche diode having a breakdown voltage at least ten times lower thanthe break-over voltage of the break-over diode.

According to an embodiment, the protection device has a breakdownvoltage ranging between 50 and 1,000 volts.

According to an embodiment, the control circuit comprises an overvoltagedetector and is capable of turning on the switch for a determined timeperiod, some time after the overvoltage will have been detected, andthen of turning off the switch after a determined time.

According to an embodiment, the control circuit comprises a detector ofthe voltage across the diode and is capable of turning on the switchwhen the voltage across the diode is within a given range, correspondingto the value of the voltage across the diode when said diode is shorted,and then of turning off the switch after a determined time.

The foregoing and other features and advantages will be discussed indetail in the following non-limiting description of specific embodimentsin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1, previously described, shows the current-vs.-voltagecharacteristic of a protection device of avalanche diode type;

FIG. 2, previously described, shows the current-vs.-voltagecharacteristic of a protection device of break-over type;

FIG. 3, previously described, shows a protection diode of break-overtype connected to a D.C. power supply line;

FIG. 4A, previously described, shows an equivalent diagram of theassembly of FIG. 3 in short-circuit;

FIG. 4B, previously described, shows the characteristic of a break-overdevice in the case of FIG. 4A;

FIG. 5 shows a first embodiment of a protection device;

FIG. 5A shows an implementation of the first embodiment;

FIG. 5B shows another implementation of the first embodiment;

FIG. 6 shows a second embodiment of a protection device; and

FIG. 7 shows an example of a circuit for controlling a protection deviceof the type in FIGS. 5 and 6.

DETAILED DESCRIPTION

FIG. 5 shows a first embodiment of a protection device. This protectiondevice comprises between two terminals A and B the parallel assembly of:

-   -   a break-over type protection diode D,    -   a switch SW, and    -   a circuit (CONTROL) for controlling switch SW.

The protection device of FIG. 5 operates as follows.

In the idle state, switch SW is off. Terminals A and B are connectedacross a D.C. power supply line so that the protection is for exampleconnected like diode D of FIG. 3. As long as the voltage betweenterminals AB remains lower than the breakdown voltage of break-overdiode D, the protection device is non-conductive. When an overvoltageappears, the protection diode becomes conductive, which results in theconfiguration of FIG. 4A, that is, the power supply connected betweenterminals AB is shorted. Once the overvoltage has passed, diode Dconducts a short-circuit current I_(DC) such as defined in relation withFIG. 4A. At this time, switch SW is turned on so that the currentbetween terminals A and B is branched by switch SW. If on-stateresistance R_(on) of switch SW is sufficiently low, the voltage betweenterminals AB becomes lower than voltage V_(h) defined in relation withFIG. 4B.

Various types of control circuits (CONTROL) may be used to control theturning on and the turning off of switch SW. Such control circuits maycomprise a processor or another timer.

According to an embodiment shown in FIG. 5A, the control circuit CONTROLis implemented by a control circuit 20A that comprises an overvoltagedetector 22 configured to detect an overvoltage at the terminal A. Thecontrol circuit 20A automatically turns on switch SW for a determinedtime period, some time after the overvoltage is detected by theovervoltage detector 22, and then turns off switch SW at the end of thetime period.

According to an embodiment shown in FIG. 5B, the control circuit CONTROLis implemented by a control circuit 20B that comprises a voltagedetector 24 for detecting the voltage across diode D. As long as thisvoltage is lower than V_(BR) and higher than V_(D), the control circuit20B will remain inactive. Then, after a first voltage drop, the controlcircuit will determine whether the voltage across diode D is within agiven range, corresponding to value V_(DC)(R_(D)/(Ri+R_(D))). Thecontrol circuit then determines the turning on and the turning off ofswitch SW.

The operation of the circuits of FIGS. 5, 5A, 5B is based on the factthat, when switch SW is in the conductive state, the voltage thereacrossdrops sufficiently to become lower than previously-defined value V_(h).This implies that on-state resistance R_(on) of switch SW must be muchlower than apparent resistance R_(D) of diode D when the device isshorted. It should be understood that this suggests to use a switch witha very low R_(on), which is not always compatible with the desire to uselow-cost switches, for example, small MOS transistors. If conditionR_(on)×I_(SC)<V_(h) is too difficult to respect, an alternativeembodiment such as illustrated in FIG. 6 may be provided.

The variation of FIG. 6 comprises the same elements as the embodiment ofFIG. 5 but further comprises an avalanche diode d of breakdown voltageV_(br), having a low breakdown voltage V_(br) as compared with breakdownvoltage V_(BR) of break-over diode D. For example, V_(br) is lower thanV_(BR)/10. The operation of the series assembly of break-over diode Dand of avalanche diode d will be little different for the absorption ofan overvoltage from the operation of diode D alone. This time, when theovervoltage has passed and the line is shorted, conditionR_(on)×I_(SC)<V_(h)+V_(br) should be satisfied, which enables to use aswitch having a higher R_(on) than in the case of the assembly of FIG.5.

FIG. 7 shows an embodiment of control circuit CONTROL. A firstcomparator COMP1 compares the voltage on the anode of the diode D toground and delivers a 1 when the voltage is positive. A secondcomparator COMP2 compares the voltage on the diode anode with athreshold V_(D) substantially corresponding to the voltage across theshorted diode and delivers a 1 when the voltage across the diode becomeslower than a value little greater than this short-circuit voltage. Theoutputs of the two comparators are sent to an AND gate having its outputcontrolling switch SW via a buffer amplifier AMP. Amplifier AMP is forexample formed of a chain of inverters in series.

Thus, switch SW is turned on for a short period when first comparatorCOMP1 has verified that the voltage across protection diode D ispositive and when this voltage becomes close to a predetermined valueV_(D). It should be noted that comparator COMP2 does not start duringthe short period which immediately follows the arrival of theovervoltage, during which the voltage briefly drops below V_(D) beforeincreasing during the absorption of the overvoltage. This results eitherfrom the fact that the comparator is not fast enough to detect thisshort transition or from the fact that the reference voltage close toV_(D) is delivered by a reference diode in parallel with a capacitorwhich branches fast transitions.

Thus, protection devices of the type described in relation with FIGS. 5and 6 have the advantages of break-over protection devices in that theyenable to use a break-over diode having a relatively small surface area,for example, 50 mm², while, as indicated previously, for protectionvoltages greater than from approximately 50 to 1,000 volts, protectionavalanche diodes should have surface areas approximately ranging from 1to 10 cm². The assembly of switching device SW, for example, a MOStransistor, and of the control circuit may for example have a surfacearea approximately ranging between 10 and 15 mm² only. Thus, the totalsurface area of the protection device is smaller than 65 mm², and thefunction ensured by an avalanche protection component having a surfacearea ranging from 1 to 10 cm² may be fulfilled. The device for examplecomprises two chips, one corresponding to the protection diode and theother to the switch and to its control circuit. These two chips may beassembled on a single support and form a simple dipole.

Specific embodiments have been described. Various alterations,modifications, and improvements will readily occur to those skilled inthe art. For example, only one-way protection diodes have been describedherein. Of course, bidirectional protection diodes (having theircharacteristics illustrated in FIGS. 1 and 2, although they have notbeen described) may also be provided.

Further, the use of the protection component in association with a linebiased to a D.C. voltage only has been described. This component mayalso be used in the case where the line is an A.C. power supply line,for example, at 50 or 60 Hz. Indeed, if the overvoltage occurs at thebeginning of a halfwave, it may be desired for the protection diode tostop being conductive rapidly after the occurrence of an overvoltagewithout waiting for the end of a halfwave, the duration of a halfwavebeing 10 ms in the case of a power supply at 50 Hz.

Such alterations, modifications, and improvements are intended to bepart of this disclosure, and are intended to be within the spirit andthe scope of the present disclosure. Accordingly, the foregoingdescription is by way of example only and is not intended to belimiting.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

What is claimed is:
 1. An overvoltage protection device capable ofprotecting a power supply line, comprising: a diode component includinga break-over diode connected between first and second terminals of thepower supply line, the diode component being configured to conduct inresponse to an overvoltage across the first and second terminalsexceeding a break-over voltage of the break-over diode; a transistor inparallel with the diode component; and a control circuit coupled to thebreak-over diode and configured to close the transistor after theovervoltage is no longer across the first and second terminals, whereinthe transistor is configured to cause the break-over diode to notconduct in response to the being closed.
 2. The overvoltage protectiondevice of claim 1, wherein the diode component includes an avalanchediode in series with the break-over diode and having a breakdown voltageat least ten times lower than a break-over voltage of the break-overdiode.
 3. The overvoltage protection device of claim 1, wherein thetransistor is a MOS transistor.
 4. The protection component of claim 1,wherein the control circuit comprises an overvoltage detector configuredto detect an overvoltage and the control circuit is configured to turnon the transistor for a time period in response to the overvoltagedetector detecting the overvoltage, and turn off the transistor when thetime period elapses.
 5. The protection component of claim 1, wherein thecontrol circuit comprises a voltage detector configured to detect avoltage across the diode component and the control circuit is configuredto turn on the transistor in response to the voltage detector detectingthat the voltage across the diode is within a given range, correspondingto a value of the voltage across the diode component when said diodecomponent is shorted, and turn off the transistor after a determinedtime.
 6. The protection component of claim 1, wherein the controlcircuit comprises: a first comparator configured to compare a voltage onan anode of the diode component to a reference voltage; a secondcomparator configured to compare the voltage on the anode with athreshold substantially corresponding to a voltage across the diode whenshorted; an AND gate having first and second inputs respectively coupledto outputs of the first and second comparators; and a buffer amplifiercoupled between an output of the AND gate and a control terminal of thetransistor.
 7. An apparatus, comprising: a power supply line; and anovervoltage protection device configured to protect the power supplyline, the overvoltage protection device including: a diode componentincluding a break-over diode coupled to the power supply line andconnected between first and second terminals of the power supply line,the diode component being configured to conduct in response to anovervoltage across the first and second terminals exceeding a break-overvoltage of the break-over diode, a transistor in parallel with the diodecomponent, and a control circuit coupled to the break-over diode andconfigured to close the transistor after the overvoltage is no longeracross the first and second terminals, wherein the transistor isconfigured to cause the break-over diode to not conduct in response tothe transistor being closed.
 8. The apparatus of claim 7, wherein thediode component includes an avalanche diode in series with thebreak-over diode and having a breakdown voltage at least ten times lowerthan a break-over voltage of the break-over diode.
 9. The apparatus ofclaim 7, wherein the transistor is a MOS transistor.
 10. The apparatusof claim 7, wherein the control circuit comprises an overvoltagedetector configured to detect an overvoltage and the control circuit isconfigured to turn on the transistor for a time period in response tothe overvoltage detector detecting the overvoltage, and turn off thetransistor when the time period elapses.
 11. The apparatus of claim 7,wherein the control circuit comprises a voltage detector configured todetect a voltage across the diode component and the control circuit isconfigured to turn on the transistor in response to the voltage detectordetecting that the voltage across the diode is within a given range,corresponding to a value of the voltage across the diode component whensaid diode component is shorted, and turn off the transistor after adetermined time.
 12. The apparatus of claim 7, wherein the controlcircuit comprises: a first comparator configured to compare a voltage onan anode of the diode component to a reference voltage; a secondcomparator configured to compare the voltage on the anode with athreshold substantially corresponding to a voltage across the diode whenshorted; an AND gate having first and second inputs respectively coupledto outputs of the first and second comparators; and a buffer amplifiercoupled between an output of the AND gate and a control terminal of thetransistor.
 13. An apparatus, comprising: an electrical componentconfigured to be coupled to a power supply line; and an overvoltageprotection device configured to protect the electrical component from anovervoltage from the power supply line, the overvoltage protectiondevice including: a diode component including a break-over diodeconnected between first and second terminals of the power supply line,the diode component being configured to conduct in response to anovervoltage across the first and second terminals exceeding a break-overvoltage of the break-over diode, a transistor in parallel with the diodecomponent, and a control circuit coupled to the break-over diode andconfigured to close the transistor after the overvoltage is no longeracross the first and second terminals, wherein the transistor isconfigured to cause the break-over diode to not conduct in response tothe transistor being closed.
 14. The apparatus of claim 13, wherein thediode component includes an avalanche diode in series with thebreak-over diode and having a breakdown voltage at least ten times lowerthan a break-over voltage of the break-over diode.
 15. The apparatus ofclaim 13, wherein the transistor is a MOS transistor.
 16. The apparatusof claim 13, wherein the control circuit comprises an overvoltagedetector configured to detect an overvoltage and the control circuit isconfigured to turn on the transistor for a time period in response tothe overvoltage detector detecting the overvoltage, and turn off thetransistor when the time period elapses.
 17. The apparatus of claim 13,wherein the control circuit comprises a voltage detector configured todetect a voltage across the diode component and the control circuit isconfigured to turn on the transistor in response to the voltage detectordetecting that the voltage across the diode is within a given range,corresponding to a value of the voltage across the diode component whensaid diode component is shorted, and turn off the transistor after adetermined time.
 18. The apparatus of claim 13, wherein the controlcircuit comprises: a first comparator configured to compare a voltage onan anode of the diode component to a reference voltage; a secondcomparator configured to compare the voltage on the anode with athreshold substantially corresponding to a voltage across the diode whenshorted; an AND gate having first and second inputs respectively coupledto outputs of the first and second comparators; and a buffer amplifiercoupled between an output of the AND gate and a control terminal of thetransistor.